[Scwm-devs] Re: question about VALIDATE macros

[Greg B. <ba...@cs...>]

So that they work as you'd expect when preceded by an if clause-- they
need to be a single statement (which many of them happen to already be,
but if the macro definition got any more complicated, they wouldn't
be).  E.g., consider:

#define DO_STUFF(x) \
   do something;
   do something else;

being used as:

if (...) 
  DO_STUFF(x)

it'll expand into:

if (...)
{
  do something;
}
do something else;

I've added braces to stress the problem.  The do/while(0) makes it work
as the user of the macro probably expected, w/o requiring her to
remember to use braces everytime she uses DO_STUFF.

I think the GNU C programming standards mention this coding style, but I
don't have a reference handy.

Thanks,
Greg


Scott Lenser <sl...@cs...> writes:

> Greg,
> 
> In the validate macros such as:
> 
> #define VALIDATE_WIN_USE_CONTEXT(win) \
>   do { if ((win = ensure_valid(win,1,FUNC_NAME, SCM_BOOL_T, SCM_BOOL_F)) == 
> SCM_BOOL_F) \
>           return SCM_BOOL_F; } while (0)
> 
> Why do they all have a do { } while(0) around the code?
> 
> Thanks.
> 
> - Scott